Method and apparatus for communication by television



Nov. 15, 1938.

A. W VANCE METHOD AND APPARATUS FOR COMMUNICATION BY TELEVISION Filed June 1'7, 1931 5 Sheets-Sheet l 210 Fl 9'. l.

RADIO TRANSMITTER MODULATOR AM F'LIFIER F I9. 3. AMPLIFIER o I v INVENTOR. I W Arthur \m. vaflcie,

a. go a2 I .6. 59 .3 F Q o I I A 4. ATTORNEY. Q

Nov. 15, 1938. A. w. VANCE 2,137,039

METHOD AND APPARATUS FOR COMMUNICATION BY TELEVISION Filed June 17, 1931 5 $heets-Sheet 2 0oon+ zsnnrmn #2355:

Nov. 15, 1938. W- VANCE 2,137,039

METHOD AND APPARATUS FOR COMMUNICATION BY TELEVISION Filed June 17, 1931 5 Sheets-Sheet 3 I VULTAGE I N VEN TOR. Arthur-W Van c e,

flg/w l8 ATTORNEY.

l l l l I l 1 1 l l VDLTABE VD LTAB E AAAAAAAA IIVIVIIIV (CZI C Nov. 15, 1938. A. w. VANCE 2,137,039

METHOD AND APPARATUS FOR COMMUNICATION BY TELEVISION Filed June 17, 1931 5 Sheets-Sheet 5 'ZOOOTURNS 7.000TIJENS 1 NVEN TOR.

ATU'IUTW Vance,

HIS A TTORNE Y.

Patented Nov. 15, 1938 um'ro STATS METHOD AND APPARATUS FOR COlVllVIUNI- CATION BY TELEVISION Arthur W. Vance, Camden, N. .L, assignor to Radio Corporation of America, a corporation of Delaware Application June 11, 1931, Serial No. 544,959

24 Claims.

My invention relates to improvements in methods and apparatus for communication by television and, more particularly, to improved methods and apparatus for synchronizing operations at the transmitting and receiving stations.

One of the objects of my inventionis to provide an improved system for communication by television having advantages over those proposed heretofore as regards the method of and means for synchronizing scanning operations at the transmitting and receiving stations.

Another object is to obtain, in a system of the characted referred to, a saw-tooth wave of the best form for scanning, and this with less power than has been the case in the various systems proposed heretofore.

Another object is to provide an improved system of the character referred to by which a picture of increased fidelity is produced.

Other objects and advantages will hereinafter appear.

In accordance with my invention, in a system for communication by television wherein a disc or other equivalent rotating means is used for scanning, and wherein horizontal synchronizing and framing frequencies are required for synchronizing operations at the transmitting and receiving station, the scanning means is utilized to develop impulses at the horizontal synchronizing frequency and certain of these impulses, occurring at the framing frequency, have a shape differing from that of the others, the diiferent shape being due to these certain impulses having a greater amplitude and/or a greater duration.

Further, in accordance with my invention, the aforementioned rotating means is utilized to develop the horizontal synchronizing frequency at an edge of the picture frame, more specifically, one of the vertical edges, and to develop the framing frequency at another edge of the picture frame, more specifically, one of the horizontal edges.

Further, in accordance with my invention, means including a single photoelectric cell are utilized to supply both the horizontal synchronizing and framing frequencies, the rotating means forming part of such means.

Further, in accordance with my invention, for the purpose of obtaining from a given voltage wave a similar current wave in any given electrical circuit, the voltage wave is utilized to force a similar current wave through a second electrical circuit whose frequency-impedance characteristic is similar to that of the first circuit, the back E. M. F. voltage across the second circult is amplified, and such amplified voltage is applied to the first circuit to cause the required current wave to pass through the same.

Further, in accordance with my invention, a saw-tooth voltage wave is developed by utilizing a thermionic tube to discharge a condenser which is continuously charged from a relatively high potential source, the tube being biased far below the cut-off point, and a dynatron oscillator is used to develop sharp voltage peaks, the tips only of which are effective to drive the tube.

Further, in accordance with my invention, a saw-tooth voltage wave is developed by using a circuit including a discharge tube and a voltage amplifier tube, and a D. C. amplifier connection is used between these tubes for impressing, on the grid of the amplifier tube, the voltage wave across the plate circuit of the discharge tube.

My invention resides in the methods of operation and in the circuits, arrangements, and constructions of the character hereinafter described.

For the purpose of illustrating my invention, several embodiments thereof are shown in the drawings, wherein- Figure 1 is a diagrammatic view of a television transmitting station embodying my invention;

Fig. 2 is a side elevational view of the scanning disc used at the transmitting station, looking toward the left in Fig. 1;.

Figs. 3 and 4 are enlarged fragmentary views looking toward the left in Fig. 1;

. Figs. 5 and 6 are fragmentary views similar to Fig. 4, illustrating modifications;

Fig. '7 is a diagrammatic view of a television receiving station embodying my invention;

Figs. 8, 9, 15, 22, and 23 are diagrammatic views of circuits proposed for use in Fig. 7;

Figs. 10 and 11 are graphical illustrations of the operating action in Fig. 9;

Figs. 12 and 13 are diagrammatic views showing proposed modifications of the circuit in Fig. 9;

Fig. 14 is a graphical illustration of the operating action in Fig. 13; I

Figs. 16 and 1'1 are graphical illustrations of the operating action in Fig.

Fig. 18 is a diagrammatic view of a proposed modification of the circuits in Figs. 9 and 15; and

Figs. 19, 20, and 21 are graphical illustrations of the principle of operation in Fig. 22.

The transmitting station shown in Fig. 1 is of the general type disclosed in the copending application of Harry H. Bates, Serial No. 445,315 filed April 18, 1930, and assigned to the Westinghouse Electric and Manufacturing Company.

' ing holes.

A scanning disc I I! is driven by a suitable constant speed motor II at 1200 R. P. M., for example, and is interposed in the usual manner between a suitable light source l2 and a lens or lens system IS. A mask is supported between the light source and disc I The disc I0 is provided, for example, with sixty scanning holes Al-An0, spirally arranged in the usual manner. The holes Aw, A1, and A2 are plugged, as indicated. The reason for this will be hereinafter explained.

Light reflected from an object l5 excites a. photoelectric cell 5, or a bank of such cells, to develop picture signals which are amplified by an amplifier l1 and applied to the input line l8 of a second amplifier l 9. The second amplifier I9 is connected, as shown, to a suitable modulator 20 which controls a radio transmitter 2|.

For the purpose of synchronizing operations at the transmitting and receiving stations, electrical synchronizing impulses, at the horizontal synchronizing and framing frequencies, are required. The present improved methods and means for developing these two frequencies will now be explained, with reference more particularly to Figs. 2 to 6.

The disc I0 is provided at the outer edge thereof with concentrically arranged holes in to (160, through which light from a light source 22 passes to a photoelectric cell 23, as shown in Fig. l. A screen 24, provided with an aperture 25 substantially equal in Width to that of the synchronizing holes, is interposed between the disc l0 and the light source 22. A lens 26 may be employed to focus the light on the photoelectric cell.

There being sixty synchronizing holes, the photoelectric cell 23 develops electrical impulses at a horizontal synchronizing frequency of 1200 cycles per second. The impulses or signals at this frequency are amplified by a suitable amplifier 21 and are supplied directly to the input line l8 of the amplifier I9, in parallel with the amplified picture signals.

The width of the opening 28 in the mask [4 is made less than the circumferential distance between adjacent scanning holes, as shown in Fig. 3, to provide for periods during which no picture signals are transmitted. The adjustment of the screen 24 is such that during these periods the synchronizing holes or to Geo move across the aperture 25.

Three picture lines are omitted by plugging holes A50, A1, and A2. The synchronizing hole 111 is equal in width to but is longer than the others, and moves across aperture 25 as the plugged hole A1 moves back of the righthand edge of opening 28.

The above construction and arrangement provides for development, at a vertical edge of the field of view, of impulses at the horizontal synchronizing frequency, and for development, at a horizontal edge of the field of view, of impulses at the framing frequency. The duration of the framing impulses is equal to that of the other synchronizing impulses because the width of hole a1 is equal to the width of the other synchroniz- The amplitude of the framing impulses, however, is substantially greater because of the greater length of hole 111.

From the foregoing, it will be seen that although the synchronizing signals are transmitted in the same channel with the picture signals, the former are developed only during periods when the picture signals are out 01f, and for this reason interfere in no way the receiving station.

When it "is desired that the framing impulses be of greater duration as well as be greater in amplitude than the other synchronizing impulses, the hole a1 in Figs. 2 and 4 is given the shape shown in Fig. 5. That is, the size and shape of, the framing hole in Fig. 5 is such that the same not only moves across aperture 25 for a longer period, but during such movement admits more light to the photoelectric cell 23 than the other synchronizing holes.

If the requirements are such that the framing impulses be of the same amplitude but of greater duration than the other synchronizing impulses, in order to distinguish the former from the latter at the receiving station, the hole 111 in Figs. 2 and 4'is given the shape shown in Fig. 6. That is, the size and shape of the framing hole in Fig. 6 is such that the same moves across aperture 25 for a longer period, and during such movement admits the same maximum amount of light to cell 23 as the other synchronizing holes.

The number of stages in amplifiers l1 and 21 is such that the output voltage of amplifier 21 is degrees out of phase with that of amplifier l1, an increase in light intensity on the picture cell l6 causing a corresponding increase, in the positive sense, in the output voltage of amplifier l1. Therefore, when the synchronizing cell 23 is exposed to the light from source 22, there is a sharp increase in the negative direction, in the output voltage of amplifier 21.

The synchronizing holes or to 1160 may be disposed on the inside of the scanning holes, if desired. It is also contemplated, if and when found desirable, to employ a separate disc for synchronizing purposes. In such case, the synchronizing disc would be driven by motor II, and provided with synchronizing holes arranged and formed as described above.

For convenience of explanation, the scanning holes A60, A1, and A: have been described as such, and it has been stated that these holes are plugged to omit several picture lines. In actual practice, however, the disc is not apertured at all at these spots.

While the scanning disc has been described as providing for 60 picture lines,- it will be understood that the design may be varied to provide for more or less lines, as might be found desirable for particular conditions. Furthermore, the scanning disc may be replaced by a scanning cylinder or other equivalent rotating means of well known construction. used, the same may be provided with the synchronizing. holes, or a separate cylinder may be employed for the synchronizing action, as explained above in connection with the disc construction.

The amplifiers I1, l9, and 20, and the usual power amplifier forming part of the radio transmitter, are of any well known construction having the following desirable characteristics:

(1) Amplification substantially constant at all required frequencies.

(2) The time-lag in the amplifiers to be either zero or substantially constant at all required frequencies.

(3) The amplification to be substantially constant at all required signal amplitudes. The modulator 20 to give practically constant modulating power over the required frequency range.

Coming now to consideration of the construction and principle of operation of the receiving with the picture fidelity at If a scanning cylinder is station, the same is shown diagrammatically in Fig. '7, and includes a cathode ray tube 35 of the general type disclosed in the copending applications of Vladimir K. Zwcrykin bearing Serial Nos. 407,652 and 504,559, and filing dates of November 16, 1929 and December 24, 1930, respectively. 7

The transmitted picture signals and the horizontal synchronizing and framing signals are received by a suitable radio receiver 36. After appropriate amplification, these signals all appear across a plurality of resistors 31, 38, and 39, each connected directly across the output line 36a. of the receiver. The picture signals are taken from resistance 31 by an adjustable Contact 40 and applied to the control grid 4| of the tube.

The grid 4| is biased negatively with respect to the cathode 42, as indicated, the negative bias being variable by the adjustable contact 43 to suit particular requirements.

The cathode 42 is indirectly heated by a suitable fllament 42a supplied withaltcrnating current at 2.5 volts.

The contact 44 is adjusted to apply to the first anode 45 a positive potential of substantially one thousand volts.

The second anode is maintainedat a positive potential of substantially five thousand volts, and comprises a silver coating 46 on the interior surface of the tube and a coating or screen 41 of fluorescent material on the end wall, the screen being electrically conductive and in electrical contact at its edge portion with the adjacent edge of the silver coating.

The electrostatic field developed by the silver coating, at the positive potential of five thousand volts. is effective to focus the cathode ray 48 to a well defined spot on screen 41. This high po tential on the silver coating and screen operates to step up the velocity of the electrons to a relatively high value, after deflection of the ray, so that the desired degree of fluorescence of the screen is obtained as the electrons strike it.

The particular values of potential given have been found to be satisfactory for successful operation, but may be varied over a wide range, as required to suit particular conditions.

For the purpose of causing the ray 48 to scan the screen 41, a 1200 cycle saw-tooth current wave is caused to pass through the horizontal deflecting coils 40, and a 20 cycle saw-tooth current wave is caused to pass through the vertical deflecting coils 50.

The reference numeral designates a system for supplying the 1200 cycle saw-tooth current wave for the coils 49. The operation of this system is controlled by and maintained in synchronism with the scanning action at the transmitting station by the received horizontal synchronizing impulses taken from resistor 39 by the adjustable contact 52.

The reference numeral 53 designates a system for supplying the 20 cycle saw-tooth current wave for coils 50. The operation of this system is controlled by and maintained in synchronism with the scanning action at the transmiting station by the received framing impulses taken from the resistor 38 by the adjustable contact 54.

. As will hereinafter more fully appear, the adjustment of the system 5| is such that it is responsive only to the received horizontal synchronizing impulses or signals, taken off at the contact 52, which are of substantially greater amphtude than the peak picture signals taken off at the contact 40, the amplitude of the peak picture signals being well below the value necessary to drive or control this system. The synchronization of the system 5| with the scanning action at the transmitting station is, therefore,

unafiected by and entirely independent of the 5 substantially greater separate the synchronizing and picture signals.

Also, the adjustment of the system 53 is such that the same is responsive only to the received framing impulses, taken off at contact 54, which are of substantially greater amplitude than the peak picture and horizontal synchronizing signals, the amplitude of the latter being well below the value necessary to drive or control this system. The synchronization of the system 53 with the framing period at the transmitting station is,

therefore, unaffected by and entirely independent of the picture and horizontal synchronizing signals, although the framing, horizontal synchronizing and picture signals are all taken directly from the output line 36a. of the receiver 36. The

purpose of making the amplitude of the transmitted framing impulses substantially greater than that of the peak picture signals and the horizontal synchronizing impulses, in this case about three times as great as the amplitude of the peak picture signals, will now be apparent. The 3 advantage of this is that no filter is required at the receiving station to separate the signals for framing from the picture and the horizontal synchronizing signals.

The operation at the receiving station is as follows. Picture signals are applied to the grid 4| to vary the intensity of the ray 48 in accordance with conditions of light and shade of the object I 5. At the completion of each pictureline, the picture signals cease due to the masking action at the transmitting station, and a horizontal synchronizing impulse occurs in each of the resistors 31, 38, and 39. This impulse is effective to synchronize the system 5|, but has no effect on the system 53 on account of the adjustment,

as explained.

The horizontal synchronizing and framing impulses swing grid 4| in the negative direction due to the fact that the amplifiers l1 and 21 at the transmitting station are 180 degrees out of phase, 55

as explained. In other words, the picture signals increase in value from a zero base line in one direction, and the synchronizing impulses are measured inamplitude from the same zero base line, but in the opposite direction. That is, in w my improved system, there is what might conveniently be termed polarity separation between the picture signals and the synchronizing impulses. The advantage of this action is that the horizontal synchronizing and framing impulses cause narrow dark borders to appear along the righthand vertical and the upper horizontal edges of the received picture, rather than bright borders of considerably greater light intensity than the picture and which would contrast unpleasantly therewith. Another advantage of this action is that the load on the transmitter is substantially lower than would otherwise be the case.

During the periods between picture frames, the framing impulses occur across each of the resistors 31, 39, and 99, and are efi'ective not only to synchronize system 5|, but also system 59 on account of their relatively great amplitude. No picture signals occur across resistors 31, 39, and 39 during these intervening periods due to the fact that the scanning holes Aim, A1, and A: are

V plugged.

Adjustment of the contact 43 operates to control the background brilliancy of the picture, while the amplitude of the picture signals applied to grid 4| is varied by adjusting contact 49.

The various circuits which I propose using for the systems 5| and 53 will now be described.

In Fig. 8 is shown a ircuit proposed for system 5|. For the purpose of obtaining a saw-tooth voltage wave, a glow tube 55 operates to discharge a condenser 56 which is continuously charged, through a high resistance 51, from a D. C. potential source, the potential in this case being 500 80 volts. The adjustment of resistor 51 and the capacity of condenser 55, for the charging potential of 500 volts, are such that the natural period of charge and discharge of the condenser is slightly lower than M second. Each received synchronizing impulse, however, taken ofl at contact 52 and applied to the glow tube through a suitable step-down transformer 58, is effective to bring the tube up to the discharge point from a point just below the same. In this way, the charge taken by the condenser is fixed, and the cycles of charge and discharge maintained at 1200 a second, in synchronism with the scanning action at the transmitting station.

The condensers 59 and 60 form a capacity potentiometer, reducing the voltage to obtain the required swing" for the grid circuit of the following screen grid tube Bl.

The 5 megohm resistor shown supplies a bias to tube 6|.

The condensers 59 and 80 are charged and discharged in the same manner as condenser 59, the

highest voltage appearing across the smallest condenser.

A circuit 62, including an inductor 63 and an adjustable resistor 64, is connected as shown in the plate circuit of tube GI.

The back E. M. F. voltage across the circuit 62 is applied to the grid of a power tube 95 which operates as a voltage amplifier.

The circuit 62 simulates the circuit comprising coils 49, that is, the resistance 94 is adjusted so that the circuit 62 has the same ratio of inductance to resistance as the coils 49. The impedance of coils 49 is greater than that of tube 85, while the impedance of the circuit 92 is less than that of tube 6|.

The operation of the circuit in Fig. 8 is as fol- .lows: A- saw-tooth =oltage wave 66, of the same shape as the saw-tooth current wave 61 required through coils 49, is generated by glow tube 55 and the associated condenser 56. This voltage wave is applied to, or drives the tube 6| which forces a corresponding saw-tooth current wave 69 through the circuit 62. The back E. M. F. voltage wave 69 across circuit 62 is of the exact shape required to pass a saw-tooth current wave, similar to wave 68, through any circuit having the same frequency-impedance characteristic as the circuit 62. Therefore, when the voltage wave 69 is applied to the grid of the voltage amplifier tube 65 and amplified, thereby to obtain the similarlyshaped but amplified voltage wave 10 in the plate circuit-of tube 65, the required saw-tooth current wave 51 will pass through coils 49. This circuit 'it should have zero and method of operation permits of the output or power tube 85 working at maximum eiiiciency.

In order that the power tube 65 can operate to maintain the voltage wave 10 across coils 49 the same as the voltage wave 69 applied to its grid,

internal resistance. The internal resistance of this tube acts very nearly the same as if it were in series with coils 49. This is compensated for by making the ratio of inductance to resistance in the plate circuit of tube 6| a little less than this ratio in coils 49.

The values of resistance, inductance, capacity, and voltage given in Fig. 8 have been found to be satisfactory for the purpose of obtaining a practically perfect saw-tooth deflection of the ray 48.

While the circuit and method of operation just described has been shown embodied in a television system to effect saw-tooth deflection of the oathode ray by electromagnetic coils, this part of my invention is of much broader adaptation, and would have utility in other environments. For example, in sound reproduction, the frequencyimpedance characteristic of output transformers and loudspeakers could be compensated for by connecting a circuit of identical frequencyimpedance characteristic in the plate circuit of a tube which would correspond to the tube 6| in Fig. 8. In such a system, the primary of the transformer, orthe actuating coilor coils of the loudspeaker, as the case might he, would be connected in the plate circuit of a voltage amplifier tube corresponding to the tube 65 in Fig. 8. In other words, the broadest aspect of this part of my invention is to obtain, from a given voltage wave of any definite, indefinite or varying shape, a current wave of the same shape through any electrical circuit or network regardless of the frequency-impedance characteristic of the latter. In accordance with my invention, this is accomplished by applying the given voltage wave to the grid of a tube, such as screen grid tube 6| in Fig. 8, to force a current wave of the same shape as the given voltage wave through a circuit connected in the plate circuit of this tube and having substantially the same frequency-impedance characteristic as a second circuit through which it is desired to pass the current wave. The back E. M. F. voltage across the first circuit-is then applied to the grid of a voltage amplifier tube. The amplified voltage wave in the plate circuit of the amplifier tube is then utilized to cause a current wave of the same shape as the original voltage wave to pass through the second circuit. In Fig. 8 the second circuit here referred to is constituted by the coils 49.

From the foregoing description of the circuit in Fig. 8, it will be apparent that the perfection of saw-tooth deflection of the cathode ray 48 by coils 49 is dependent upon the perfection of the original saw-tooth voltage wave 66.

In the circuit shown in Fig. 9, the various parts which are the same as or correspond to equivalent parts in Fig. 8 are designated by the same respective reference numerals as the latter. From this it will be seen that in Fig. 9, the circuit from condenser 56 on through to the deflecting coils 49 is the same as this portion of the circuit in Fig. 8. In Fig. 9, however, the means for generating the original saw-tooth voltage wave is different, and includes an additional condenser II which is continuously charged from the 500 volt supply through a high resistance 12. The voltage on the condenser 1| increases until the breakdown voltage of a suitable glow tube 73 is 75 2,137,039 reached. The breakdown periods of the tube 18 are controlled by and occur with the received synchronizing impulses taken from the resistor 39 by the contact 52.

When the tube 13 breaks down to discharge the condenser 1 I, a heavy current is sent through theinductor II. The steep wave front of the current through the inductor 14 causes a high voltage to be suddenly developed across the same, the voltage wave having substantially the shape shown in Fig. 10.

The discharge tube 55a for the condenser 56 is shown as a screen grid tube, and corresponds to the glow tube 55 for discharging this condenser in Fig. 8. The discharge tube 55a is biased far below cut-off to a point whereat it will require, for the purpose of swinging" the grid of this tube, a positive voltage at least as high as that designated by the dash line 15 in Fig. 10.

The condenser 56 continues to acquire a charge until it is discharged by the discharge tube 55a. The adjustment of the resistor 51, the capacity of condenser 56, and the charging voltage are such that, within the range of the condensercharging curve used, the voltage across the condenser increases substantially linearly with respect to time. When one of the steep impulses l6 swings the grid of tube 55a positive, the latter instantly becomes efiective to discharge condenser 56, and continues to do so for the period of time'during which the voltage wave in Fig. 10 is above line 15, after which the condenser again starts to acquire a charge substantially linearly with respect to time. A saw-tooth voltage wave 18 is thereby obtained across the condenser 56, asis more clearly shown in Fig. 11 wherein the effective tip portions TI of the voltage impulses 76 are shown on the time axis at the discharge periods.

From the foregoing, it will be seen that the length of return time of the saw-tooth wave 18 is determined by the time period t, since the condenser 56 is, at all other times, charging. The return time of the voltage wave 18 is, therefore, very substantially shorter than could possibly be the case for the saw-tooth voltage wave 66 generated in Fig. 8 by the glow tube 55 and the associated condenser. It will be seen further that, in Fig. 9, adjustment of the condenser 56 and the resistor 51, so that the condenser charges on the most advantageous portion of the charge curve, has no effect upon the speed or frequency of the saw-tooth wave developed.

The operation of the circuit in Fig. 9 from the condenser 56 to the deflecting coils 49 is the same as that in Fig. 8.

As in Fig. 8, the values of resistance, inductance, and capacity designated in Fig. 9 have been found to be satisfactory for successful operation.

Any voltage wave having a sharp peak may be used to drive tube 55a.

A grid glow tube, a thyraton, or any other suitable discharge device may be substituted for the glow tube 13. For example, Fig. 12 shows the manner of connecting a grid glow tube 13a 'in the circuit shown in Fig. 9 to replace and serve the same purpose as the glow tube I3.

As shown in Fig. 13, a resistance 14a may be used instead of the inductor 14 in Fig. 9, in which case the shape of the voltage wave would be substantially as shown in Fig. 14. In- Fig. 14, the top portions 19 of the impulses serve the same purpose as the top portions ll of the impulses in Fig. 10.

For the purpose of developing voltage peaks to drive the tube 55a in Fig. 9, it is proposed in some cases to substitute, for the glow tube 13 and its associated parts, a dynatron oscillator 80, as shown in Fig. 15, in which the various parts corresponding to similar parts in Fig. 9 are designated by the same respective reference numerals as the latter. The oscillator 88 is a tube of the screen grid type, the resistance contacts 8| and 82 being adjusted so that the tube is selfoscillating. The value of the inductance 83 in the plate circuit and the potential on the plate are made such that the tube is self-oscillating at some frequency below the required horizontal synchronizing frequency of 1200 cycles. The received synchronizing impulses taken from the resistor 38 by the contact 52 and applied to the grid of the tube through a suitable step-up transformer 84, drive the tube and maintain its frequency of oscillation at the frequency of these impulses which, in this case, is 1200 cycles. As an alternative, it is proposed to adjust the plate potential and make the value of the inductance 33 such that the tube '80 is just below the point of self-oscillation. The received synchronizing impulses then drive the tube as before, to maintain the same in oscillation at the frequency of these impulses. In either case, a current wave roughly approximating a saw-tooth, as shown in Fig. 16, is obtained in the inductor 83. This current wave has a very short return period t, and causes a voltage wave of substantially the shape shown in Fig. 1'7 to develop across inductance 83. The amplitude of the peaks 85 of the voltage wave is proportional to the slope of the return line of the current wave, and their period of duration is equal to the return period t of the current wave. The return period t is so short that voltage peaks of great magnitudes are generated, voltages as high as 5,000 volts being possible with use of screen grid tubes of usual construction. From this it will be seen that the discharge tube 55a. in Fig. 15 can be biased much farther below cutoff than is possible in Fig. 9, so that it requires a relatively higher positive voltage to swing the grid, the value of this voltage being indicated by the dash line 86 in Fig. 1'7. Since only the tip portions 81 of the peaks 85 are efiective to swing the grid, it will be seen that the discharge period of tube 550 in Fig. 15 is only a friction of the short return period t. Tube 55a in Fig. 15, therefore, discharges condenser 56 only an infinitesimal period of time, so that a very favorable saw-tooth voltage wave is obtained, the ratio of the charging period to the discharging period being considerably higher than is the case in the circuits in Figs. 8 and 9.

As shown, the voltage was across inductor 83 in Fig. 15 is applied to the grid of tube 55a by a coil 83a. inductively coupled to coil 83.

Fig. 18 shows a proposed D. C. amplifier connection between the discharge tube 551:. and the tube 6| in Figs. 9 and 15, whereby the condensers 59 and 60 and the resistor 88 are eliminated. In this connection, a self-biasing resistor 89 raises the potential on the cathode of tube 61 positive with respect to ground by an amount equal to the D. C. component of the voltage on condenser 56 plus the normal bias voltage for tube 6|. The condenser 56 is made just large enough so that the tube 55a discharges the same only enough to give the required swing on the grid of tube 6|. By varying the charging resistor, as well as the capacity of condenser 56, this swing may be placed on the most advantageous portion of the charging curve, whether linear or curvilinear.

The D. C. amplifier connection in Fig. 18 has been found to contribute toward more linear sawtooth waves and, correspondingly, better scan-' ning than has been obtained with the connection shown in Figs. 9 and 15 between tubes 55a and BI.

Fig. 21 shows the approximate voltage wave shape that is required across a circuit, comprising an inductor and resistor in series, to cause a saw-tooth current wave to pass through the same. The voltage wave 19 in Fig. 8 has this shape. In Fig. 21, the amplitudes of the parts A and B of the wave are determined by the length of return line of the saw-tooth current wave and by the ratio of inductance to resistance in the circuit, such as the coils 49 in'Figs. 8, 9, and 15.

When the charging voltage supply for the condenser 59 is many times the voltage to which it charges before being discharged, the wave shape of the A. C. component of the voltage on the condenser is a linear saw-tooth, as shown in Fig. 19. Furthermore, the current wave in the plate circuit of the discharge tube, such as tube 55a in Figs. 9 and 15, is an impulse wave such as is shown in Fig. 20, the impulses occurring during the return line periods tr of the voltage wave in Fig. 19.

From the foregoing it will be'seen that if the current wave in Fig. 20 were a reversed voltage wave, and if such a voltage wave be added to the voltage wave in Fig. 19, the resultingvoltage wave will have a shape very similar to that shown in Fig. 21, and which is required to pass a sawtooth current wave through a circuit having the same frequency-impedance characteristic as the coils 49 in Figs. 8, 9, and 15. For the purpose of accomplishing this, the circuit shown in Fig. 22 is proposed. In this circuit a dynatron oscillator 90, corresponding to the oscillator in Fig. 15, operates in the same manner as the latter to supply sharp voltage peaks for driving a discharge tube 9l which corresponds to and operates in the same manner as the discharge tube 55a in Fig. 15 to develop across a condenser 93 a sawtooth voltage wave as shown in Fig. 19. An impulse current wave, as shown in Fig. 20, occurs in the plate circuit of tube 9|, and by interposing a resistance 94 between condenser 93 and the'plate of tube 9i, a reversed impulse voltage wave is developed from this current wave and added to the saw-tooth voltage wave to obtain the required voltage wave in Fig. 21. This required voltage wave is applied to the grid of a voltage amplifier tube 95 corresponding to tube 95 in Fig. 15, and is amplified and applied to the deflecting coils 49 to cause the required saw-tooth current wave to pass no tube, such as the tube Si in Figs. 8, 9, and 15,

is required. A further advantage resides in the fact that no compensating inductor, such as the inductance 63 in Figs. 8, 9, and 15, is required. In these figures, the inductance 63, tuned with the capacity of'the tube 6| interconnected with it, and its own distributed capacity, is detrimental satisfactory solution to the obtaining of good saw-tooth waves above a certain frequency range. As there is no such inductance in Fig. 22, there is no such i'requency limitation in this circuit. Still another advantage of the circuit in Fig. 22 resides in the fact that the conditions of polarity are such as to swing" the power. amplifier tube 95 in a favorable direction so that more usable power can be obtained from this tube than would otherwise be possible.

Each of the circuits in Figs. 8, 9, 15, and 22 are particularly adapted for the horizontal defiection system 5| in Fig. '7.

Each of the deflecting circuits shown in Figs. 8, 9, 12, 13, 15, 18 and 22' is characterized by the fact that it is eflfective to cause a saw-tooth current wave, at a frequency of at least one thousand cycles, to pass through the high impedance electromagnetic windings 49 for horizontal deflection of the cathode ray. It is important to understand that for this purpose each p of these circuits is effective to generate the required shape of voltage wave described, and that in dealing with high impedance electromagnetic windings for deflecting the ray at least one thousand times a second, the required shape of voltage wave' is substantially different from the sawtooth shape deslred for the current wave. In other .words, my improved circuits represent a of the problem of causing a saw-tooth current wave at a relatively high frequency to pass through electromagnetic defleeting coils or windings of relatively high impedance. Each of these circuits embodies a relaxation oscillator circuit, including the respective tubes 55, 13, 13a, 89, 55a and 90.

A circuit proposed for the framing or vertical deflection system 53is shown in Fig. 23. In this circuit, a condenser 96 is continuously charged through a high resistance 91 from a source of high positive potential. A grid glow tube 99 operates, under control of the relatively strong framingimpu'lses received and taken from resistance 39 by contact 54, to discharge the condenser and develop a saw-tooth voltage wave across the same of the same Irequency as the con-- trolling impulses which, in this case, is 20 cycles. This voltage wave is applied to the grid of a current amplifier tube 99 to cause a saw-tooth current wave to pass through the deflecting coils 50 connected in the plate circuit of this tube.

The bias on the grid of the discharge tube 99 is such that the same is brought up to the breakdown point only by voltage impulses of an amplitude at least as great as is occasioned by the relatively strong framing impulses received. It will, therefore, be understood that the received horizontal synchronizing impulses, which control or drive the system 5| for horizontal deflection of the ray 48, are ineffective with respect to the system 53 for the vertical deflection.

It is proposed in some cases to substitute for the capacitive coupling. shown between the discharge tube 98 and amplifier tube 99, the D. C. amplifier connection shown in Fig. 18.

While the various values of inductance, resist ance, capacity, and potential appearing in Figs. 8, 9, 15, 22, and 23 have been ioundto be satisfactory for successful operation, it will be understood that the same have been given by way of example only, and that they are not critical in any strict sense of the word and can be varied over a substantial range.

The manner of operating the receiving station is as follows, assuming that the circuit in Fig. 22

is used for the horizontal deflection system II, and the circuit in Fig. 23 is used {or the vertical deflection system 53.

The resistance contact 43 is adjusted to vary the picture signal intensity until some visual in-' dication is obtained on the screen 41. The frequency of the dynatron 90 is then adjusted so that the picture looks in step, as denoted by the picture remaining in place horizontally. The vertical saw-tooth frequency is then adjusted, by means of the charging resistor 91, until the picture remains in place vertically. For final adjustment of the synchronizing action, the horizontal and vertical synchronizing controls are varied until the picture is steady.

Too weak a synchronizing signal is indicated by a tendency of the picture to be unsteady. This condition is corrected by adjusting the contacts 52 and 54. If the vertical synchronizing signals are too strong, the picture will fold-up and tend to synchronize at some multiple of the proper synchronizing frequency; the contact 54 is then retarded until this condition is corrected.

If the horizontal synchronizing signals are too strong, the picture will be ragged along the edges thereof; this is corrected by retarding the control contact 52.

When the picture is properly synchronized, and the intensity control contact 33 adjusted to the desired point, it will be found that the three control contacts 43, 52, and 55 for the respective 1 picture and synchronizing signals are not interrelated, but that each operates independently of any control effect which would occur upon operation of the others. The entire adjustment of the system is, therefore, comparatively easy.

When the shape of the framing hole at the transmitting station is as shown in Fig. 5, the system 53 at the receiving station for vertical deflection of the ray is adjusted so that the same is responsive to an impulse which has either a greater amplitude or a greater duration than the horizontal synchronizing impulses. When the construction in Fig. 6 is used, the adjustment of system 53 is such that the same is responsive only to the received framing impulses of substantially greater duration than the other impulses.

The term dynatron or dynatron oscillator in the claims is used in the broad sense, and is intended to embrace a suitable thermionic device adjusted to be self-oscillating at some suitable frequency, or such a device having its frequencydetermining circuit tuned to a desired frequency and adjusted at or in proximity to the point of self-oscillation, or at least close enough to such point so that received synchronizing signals are effective to cause the device to oscillate at the required frequency.

The terms drive" or swing in the claims refer to the condition where an impulse is applied to an electrode of a thermionic device to make the same conductive or, in other words, to cause the device to draw plate current.

The terms current wave and voltage wave", as used in the specification and claims refer, strictly speaking, to the shapes of the curves or graphs obtained when voltage and current values are plotted against time. The term return period of a voltage or current wave, as used in the specification, refers to the period of time during which the voltage or current decreases from the maximum to the minimum values. In Fig. 16, for example, the return period of the current wave is designated by t, the value of which is determined by the projection of the return line of the graph on the time axis. The return line of the current graph is, for convenience in explaining the operating action, referred to as the return line of the current wave.

It is contemplated, in some cases, todeflect the ray 08 by electrostatic means, in which case suitable deflecting plates would be substituted for the coils shown, and the developed saw-tooth voltage waves applied directly across these plates.

Furthermore, it is seen that various changes can be made such as in the size, shape and arrangement oi the parts, and in thevalues of inductance, resistance, capacity and supply voltages without departing from the spirit of the invention or thescope of the claims.

I claim as my invention: I

1. In television transmission apparatus photoelectric means, a scanning disc having a plurality of apertures, one of said apertures being able to pass a greater amount of light flux therethrough than the remaining apertures, a light source positioned so as to impress light onto the photoelectric means in accordance with the size of the aperture in the disc as it is rotated, and means 'for rotating' said disc whereby the light supplied to the photoelectric means by said light source causes the generation of a series of reoccurring impulses for synchronizing purposes and wherein some of said impulses have a greater amplitude than others.

2. In television transmission apparatus photoelectric means, a scanning disc having a plurality of apertures, at least one of said apertures being of the same width and a greater height than the remaining apertures, a light source mounted so as to supply light to said photoelectric means in accordance with the size of the apertures in said disc during rotation of the disc, and means for rotating said disc whereby there are generated by the photocell reoccurring impulses for synchronizing purposes and wherein all of said pulses are of substantially the same duration and some of said impulses are of greater amplitude than the others.

3. In television transmission apparatus photoelectric means, a scanning disc having a plurality of apertures, one of said apertures being of greater width and greater height than the remaining apertures, a light source mounted so as to supply light to said photoelectric means in accordance with the size of the apertures in said disc during rotation of the disc, and means for rotating said disc whereby there are generated by the photocell reoccurring impulses for synchronizing purposes and wherein some of said impulses are of greater duration and greater amplitude than the others.

4. In a system for television wherein picture signals and synchronizing signals are required, means for developing the picture signals, means for developing diiIering sets of synchronizing signals, said difiering'sets of synchronizing signals having diiferent amplitudes, a phase reversal means connected to one of said signal developers,

and means for mixing said picture signals and said sets of synchronizing signals whereby the picture signals and synchronizing signals are of opposing polarity, the synchronizing signals being of the same polarity, but diiferent sets of synchronizing signals being of different amplitude;

5. In a system for television, a cathode ray tube, electromagnetic means for deflecting the ray, a thermionic device having a grid, means for applying to said grid a saw-tooth voltage wave, an electrical circuit connected in the plate circuit of said device, and an amplifier tube having the plate circuit of said tube, said electrical circuit having a frequency-impedance characteristic substantially opposite to such characteristic of said electromagnetic means.

6. In a television system, a cathode ray tube, electromagnetic means for deflecting the ray, a condenser, means for continuously applying to said condenser a uniform charging voltage, a thermionic tube biased below cut-01f and operable to discharge said condenser, means for applying to the grid of said tube regularly reoccurring electrical impulses above the cut-off point, an electrical circuit connected in the plate circuit of said tube, and an amplifier tube driven by the back E. M. F. voltage across said electrical circuit, said electromagnetic means connected in the plate circult of said amplifier tube, the frequency-impedance characteristic of said electrical circuit being substantially opposite to such characteristic of said electromagnetic means.

7. In a television system wherein picture and horizontal synchronizing and framing signals are required for operation of the receiving station, means forming part of the transmitting station for generating said three kinds of signals, the

framing signals being substantially greater in intensity than the horizontal synchronizing and the peak-picture signals, the horizontal synchronizing signals being substantially greater in intensity than the peak-picture signals, radio receiver means forming part of the receiving station for intercepting the transmitted signals; first, second, and third resistances each connected independently of each other across-the output side of said receiver means; picture-developing means supplied with picture signals from the first resistance, scanning apparatus supplied with horizontal synchronizing signals from the second resistance, and framing apparatus supplied with framing signals from the third resistance.

8. In a television system wherein a saw-tooth current wave is to be passed through electromagnetic ray deflecting means for the purpose of linearly deflecting said ray, means for linearly charging a condenser, a thermionic discharge tube connected to said condenser and forming a discharge path therefor, means for periodically rendering the thermionic tube conductive, and means for adding to the voltage wave across said condenser a voltage wave similar to the occurring current wave through the tube forming the discharge path for said condenser.

9. In a television system, electromagnetic means for efiectingscanning action at the receiving station, a voltage amplifier tube, said electromagnetic means connected in the plate circuit of said tube, a condenser connected in the grid circuit of said tube, means for developing a sawtooth voltage wave across said condenser, and capacitative means connected in one of said circuits of said tube for reshaping said voltage wave to a voltage wave shape efiective to cause a sawtooth current wave to pass through said electromagnetic means.

'10. In a television system, an electron device provided with screen structure and with means for developing a beam of electrons directed at said structure, and means for deflecting said beam, said deflecting means including an electromagnetic winding and means for causing a substantially saw-tooth current wave at a frequency of at least one thousand cycles to pass through said winding; said last-named means including a relaxation oscillator circuit comprising a con- 2,187,039 a grid, said electromagnetic means connected in denser-discharge tube provided with a grid, means supplying the grid of said tube with a negative biasing potential substantially greater than the negative potential for cut-oii', and a dynatron oscillator supplying voltage peaks to the grid circuit of said tube wherein the tip portions only of said peaks are effective to cause said tube to draw current.

11. In a television receiving system, a cathode ray tube provided with a fluorescent screen and with means for developing a ray of electrons directed at said screen, means for deflecting said ray, said deflecting means including an electromagnetic winding and means for causing a substantially saw-tooth current wave at a frequency of at least one thousand cycles to pass through said winding; said last-named means including a relaxation oscillator circuit embodying a' condenser-discharge tube provided with a grid, means supplying the grid of said tube with a negative biasing potential substantially greater than the negative potential for cut-01f, and a thermionic tube supplying voltage peaks to the grid circuit of said condenser-discharge tube wherein the tip portions only of said peaks are effective to cause condenser-discharging action of said tube; and means for controlling operating action of said thermionic tube in accordance with received synchronizing electrical effects.

12. -In a system of the character described, an electron device provided with means for developing a beam of electrons, and means for deflecting said beam; said deflecting means including an electromagnetic deflecting coil, and a relaxation oscillator circuit for developing a voltage wave form effective to cause a saw-tooth current wave to pass through said coil; said circuit comprising a thermonic condenser-discharge tube biased be low the cut-oil? point and having a substantially non-inductive plate circuit, and a condenser and a resistance connected in series, the condenserresistance series being connected across the plate circuit terminals of said tube.

13. In a system of the character described, an. electron device provided with means for developing a beam of electrons, means including an electromagnetic coil for deflecting said beam, and means for causing a saw-tooth current wave at a frequency of at least one thousand cycles to pass through said coil, said last-named means embodying a relaxation oscillator circuit for developing a voltage wave at such frequency and of a form effective to cause said saw-tooth current wave to pass through said coil; said circuit comprising a thermionic condenser-discharge tube biased below the cut-off point and having a substantially non-inductive plate circuit, and a condenser and a resistance connected in series, the condenserresistance series being connected across the plate circuit terminals of said tube.

14. In a system of the character described, an electron device provided with means for developing a beam of electrons, and means for deflecting said beam; said deflecting means including an electromagnetic deflecting coil and a circuit for causing a saw-tooth current wave to pass through said coil; said circuit including a network comprising a resistance and a condenser connected in series therewith, and a thermionic device for forcing a series of similar voltage impulses across said of the impulse voltages may be added to the sawtooth voltage wave.

15. In a television system, an electron device, electromagnetic means associated with said device for deflecting the electrons, and means for causing a saw-tooth current wave to pass through said electromagnetic means; said last named means comprising an electrical circuit embodying an electron tube, and an electrical network connected in the output circuit of said tube and comprising a condenser and a. resistance, said condenser and said resistance being connected in series relation to each other, said tube operating to develop across said network a voltage wave comprising a saw-tooth component appearing across said condenser and an impulse component appearing across said resistance. 4

16. In a deflecting circuit of the character described, an inductive circuit, and means for causing a saw-tooth current wave to pass through said circuit; said last-named means comprising an electrical circuit embodying an electron tube, and an electrical network connected in the output circuit of said tube and comprising a condenser and a resistance, said condenser and said resistance being connected in series relation to each other, said tube operating to develop across said network a voltage wave comprising a sawtooth component appearing across said condenser and an impulse component appearing across said resistance.

17. In a deflecting circuit for deflecting a cathode ray beam, an inductive circuit for deflecting said beam, a condenser, means for linearly charging said condenser means for linearly discharging said condenser whereby said charging and discharging cause a saw-tooth voltage wave to be impressed across said condenser, a resistance connected in series with said condenser, means for impressing on said resistance a voltage impulse of a substantially saw-tooth shape, and means electrically connecting said inductive circuit to the condenser and resistance.

18. A system for deflecting electron passage in a cathode ray tube, comprising in combination a cathode ray tube provided with electron passage deflecting elements, saw tooth voltage generating means consisting of a condenser connected with a direct current source to be charged thereby at a constant 'rate and a vacuum valve having an anode, at least one grid and a cathode, said anode and cathode being connected to the terminals of said condenser respectively for short circuiting said condenser periodically, and means for generating periodical impulses from an independent oscillator which are supplied to said grid of said short circuiting valve to control the discharge of said short circuiting valve.

19. In a "sweep" circuit for the deflection plates of a cathode ray oscillograph, a condenser included in said circuit, means for charging said condenser !rom a source 01' current at a constant rate, -a. vacuum tube having at least three elements therein, its plate-fllament circuit being connected across said condenser, means for maintaining the grid of said tube highly negative while said condenser is being charged, and means for rapidly driving the grid positive long enough to discharge the condenser through the tube as and for the purpose described.

20. In a "sweep" circuit for the deflection plates 'of a cathode ray oscillograph, a condenser included in said circuit, means for charging said condenser from a source of unidirectional current at a constant rate, and means including, flrstly a.

hard tube for discharging said condenser at a high rate of speed, and secondly, an oscillator delivering a peaked voltage directly to the grid of said hard tube for the control thereof.

21. In a system for deflecting an electron beam in a cathode ray tube, a storage element and means in combination therewith for charging and discharging said storage element at materially different rates of charge and discharge, an electron discharge device having a control electrode energized from said storage means, a thermionic amplifier connected to the electron discharge device, an output circuit connected to the thermionic amplifier and a predistorting capacitative network connected between the electron discharge device and the thermionic amplifier.

22. In a television system wherein picture and horizontal synchronizing and vertical synchronizing signals are required for operation of the receiving station. means forming part of the transmitting station for generating said signals, one of said synchronizing signals being generated substantially greater in intensity than the other of said synchronizing, signals, receiver means forming part of the receiving station for intercepting the transmitted signals, and amplitude selection means associated with said receiver means for separating the horizontal synchronizing signals from the framing synchronizing signals.

23. In a television system wherein picture and line synchronizing and framing signals are required for operation of the receiving station, means forming part 01' the transmitting station for generating said signals, one of said synchronizing signals being generated substantially greater in intensity than the other of said synchronizing signals, receiver means forming part oi the receiving station for intercepting the transmitted signals, a channel selective to the amplitude of one of said synchronizing signals, and a second channel adapted to convey the other of said synchronizing signals to a utilization circuit.

.24. In a television system wherein video and line synchronizing and trame synchronizing signals are required for operation oi. the receiving station, means forming part of the transmitting station for generating said signals, the frame synchronizing signal being generated substantially greater in intensity than the line synchronizing signal and the video signals, receiver means forming part of the receiving station for intercepting the transmitted signals, a channel adapted to be actuated by the frame synchronizing signals, only, a second channel adapted to be energized by the line synchronizing signals, and a third channel adapted to be energized by the video signals.

- ARTHUR W. VANCE. 

